Gamma Controls are required to achieve optimal light output at each measured step between video black and reference white.
Gamma refers to the change in light output as the video signal increases from one reference level to the next, as measured in IRE units. The gamma response is typically checked at each 10-IRE step from 0 (video black) to 100 IRE (reference white), but it is also possible to measure and report gamma response in 5- or even 1-IRE increments.
According to the Society of Motion Picture and Television Engineers (SMPTE) standard, the correct gamma response is 2.2 at each step. In real world applications, a display gamma ranging from 2.2 to 2.5 is desired, and this may vary according to the display technology deployed and viewing environment.
A gamma that is too low overall will contribute to images appearing too bright, with a flat, dull or washed out appearance; displays with a gamma that is too high will produce images that appear too dark, with a lack of dynamic range, possibly including "crushed" shadow detail.
While picture gamma is generally referred to as an overall measure across the grayscale range, extreme gamma errors that occur at isolated areas along the gamma curve can also adversely impact overall image quality.
Setting contrast and brightness correctly is a key component in achieving proper gamma response, as these settings have a significant influence on the extreme ends of the gamma curve, while the supporting gamma controls allow adjustment of specific portions of the grayscale range between video black and reference white.
Some external video processors or scalers include additional controls that allow adjustment at specific or user-selectable points on the gamma curve.